The β-adrenergic receptors are members of the super-family of G protein-coupled receptors and mediate responses to external ligands, particularly epinephrine and norepinephrine, by coupling the stimulation of Gαs to the activation of adenylyl cyclase, resulting in increased intracellular second messenger cAMP. Three subtypes of β-adrenergic receptors are known. The β1-receptor is expressed primarily in the heart, coronary artery, kidney, muscle, and central nervous system and affects cardiac stimulation, coronary vasodilation and relaxation of the colon and esophagus. Polymorphisms in the β1-receptor are associated with several forms of hypertension and heart failure and effects on resting heart rate. The β2-adrenergic receptor is found in the lungs, gastrointestinal tract, liver, uterus, vascular smooth muscle, heart and skeletal muscle, where it regulates, in part, smooth muscle relaxation (e.g., bronchodilation). The β3-adrenergic receptor is expressed primarily in adipose tissue (brown and white), urinary bladder, gallbladder, colon and heart.
There is differential, species specific expression of the various adrenergic receptor subtypes, suggesting the role of different subtypes in the same tissue of different species. In humans, the β3-adrenoreceptor is expressed in the urinary bladder detrusor, and the β3-adrenergic receptor mRNA is the predominant mRNA in patients undergoing radical cystectomy. Moreover, β1 and β2 selective agonists have no effect on detrusor function while β3-selective agonists produce concentration-dependent relaxation (Igawa Y. et al., 1999, Br J Pharmacol. 126:819-25). These observations have led to the development of β3-adrenoreceptor agonists for treatment of various forms of overactive bladder syndromes (see, e.g., Igawa Y. et al., 2010, Korean J Urol. 51:811-818). 33-adrenoreceptor specific agonists based on hydroxymethyl pyrrolidines are described in WO2009124167 and WO 2009124166. Synthesis of the hydroxy pyrrolidine drug can use intermediates having the structures (a) and (b), where Ar represents an aryl group and R10 and R11 represent protecting groups.

The intermediate (a) exists as cis and trans isomers that must be separated and purified to obtain chiral intermediates for synthesis of the final drug product. The synthetic route for obtaining intermediate (b) uses the starting compound 5-hexynoic acid and reaction with either (S)-(−)-4-benzyl or (S)-(−)-4-phenyl-2-oxazolidinone to set the chirality of the hydroxyl group and the left side of the pyrrolidine group (see, e.g., WO2009124167 and WO 2009124166, incorporated herein by reference).
In view of the need for separation of chiral intermediates or use of chiral specific agents for synthesis of β3-adrenoreceptor agonists, it is desirable to find alternative synthetic routes, particularly processes that result in high diastereomeric excess of specific stereoisomers of interest, provide efficient conversion of starting material to desired product, use mild conditions, and avoids use of chiral specific chemical agents.